Yes it is a problem from a couple of POVs. First, assuming it was used because dough in pH was too low, it doesn't raise it fast enough to set pH within the desired range for the first set of enzymes (be they beta glucanases, proteases or amylases). But chalk is the gift that keeps giving. Over time more and more acid is neutralized and the pH continues to rise. Beta glucanase rest pH might be too low, saccharification pH or kettle pH may be too high. pH in the fermentor may be too high (i.e. high to the point that the yeast have establishing the pH they need.

As I have said many times before if one's mash pH is 5.0 or less something is wrong. Look to recipe, the means being used to measure pH etc to determine what it is. If you, with open eyes, use enough black malt or accidentally put in enough sauermalz to get the pH down to 5.0 or less then neutralize it with lime or sodium carbonate.

Yea I used a calibrated PH meter so it's probably accurate. What can be expected with a PH this low?

I can't answer that question as I have never, in 30 years of brewing, managed to get myself into this situation. We can, of course, assume, that efficiency may be down but I wouldn't expect that to be by much. It isn't efficiency considerations that drive one to strive to hit a particular pH so much as it is the fact that at the right pH all the 'flavors become brighter'. I understand what that means in terms of pH too high (which I have experienced) but don't know what the effects would be if it is too low. Sub optimal, whatever that may mean.

Given that mash pH is too low you can certainly expect that kettle pH will be too low and a probable manifestation of that would be lower hops utilization. With the extra acidity the yeast will have an easier job of establishing the fermentation pH they want. Will they undershoot so the fermentation is impaired? Intuition says no - they will just secrete less acid than they normally do but I have nothing substantive to back that intuitive feel up.

I just tuned in as I am mashing a Robust Porter. This is a great discussion (as all water discussions are when AJ weighs in.)

I have a 16.5 gallon mash going right now at about 1.78 qt/lb dough in for a porter. My initial pH (~70F) was a bit low at 5.0. I've added 4g of CaCO3 and watched its risen to 5.4. Everything tastes good. I have not used any CaCO3 in the past, but it seemed to do the job (a bit slowly.)

My pH meter was calibrated (2-points) before I mashed. I think this gives me about a 5.1 mash pH in the mash tun. I plan to add small amount of CaCL in the boil just to bump my chloride a little and be done with it.

I have pretty good notes and am happy to post my recipe and calculated guess at my water profile (since it has not been tested recently).

I just tuned in as I am mashing a Robust Porter. This is a great discussion (as all water discussions are when AJ weighs in.)

I have a 16.5 gallon mash going right now at about 1.78 qt/lb dough in for a porter. My initial pH (~70F) was a bit low at 5.0. I've added 4g of CaCO3 and watched its risen to 5.4. Everything tastes good. I have not used any CaCO3 in the past, but it seemed to do the job (a bit slowly.)

My pH meter was calibrated (2-points) before I mashed. I think this gives me about a 5.1 mash pH in the mash tun. I plan to add small amount of CaCL in the boil just to bump my chloride a little and be done with it.

I have pretty good notes and am happy to post my recipe and calculated guess at my water profile (since it has not been tested recently).

Mostly I wanted to chime in and say thanks. This is a great thread.

AJ - if you are still following this thread, do you think the small amount of CaCO3 added to my mash is likely to have any detrimental effects? I was just curious. Thanks.

1. It raises mash pH which is in many cases something you do not want to do. Most of the effort brewers make in treating their water is aimed at lowering alkalinity and thus mash pH.

2. Where alkalinity is required chalk is a poor source because of the long reaction time. You add chalk and the pH goes up so you think you have succeeded and move on with the mash but in fact only a portion has reacted so that as you continue the mash chalk continues to dissolve and the pH continues to rise. Ca(OH)2 is a better choice from this perspective as it reacts quickly.

I would not add chalk to mash. If I want carbonate based alkalinity (which I rarely do) I add chalk to the water and bubble CO2 through the water. This makes sure that the water reaching the grain contains calcium bicarbonate as it would in a naturally alkaline water. The reactions will be quick in such a case as the chalk is already dissolved.

Thanks AJ, I added 2 g and checked the pH a couple times. It stayed at 5.2 so I took a chance and added 2 more grams and after 15 min it was 5.4. My mash was a constant recirc. The final runnings pH were also 5.4 I believe. It certainly may have gone over, but it was slow and I missed it if it did. That amount of CaCO3, based on my water and the SRM of the beer, seemed to get it a little closer on Palmer's spreadsheet as well, but I did not really worry too much about it. I really just wanted to add a little calcium and that seemed to be the best form to do so in light of the mash pH. D

Do you think a 5.0 pH at room temp would have been a better solution for a dark beer like a porter? I know you do not have the reicpe and water profile to base it on, but I was curious your thoughts on tackling the lower pHs that can be seen in darker beers.